Resumo

Background. Bloodstream infections (BSI) are a worldwide concern impacting health care-associated morbidity, mortality and the cost of care. Early detection of the BSI is crucial in the clinical setting. Traditional identification requires the sub-culture of signaled blood culture broth with identification available only after 24-48 hours. Matrix-assisted laser desorption ionisation/time-of-flight mass spectrometry (MALDI-TOF MS, VitekMS®, BioMérieux) is a rapid and easy-handle methodology to identify bacterial isolates. The application of MALDI-TOF MS directly from blood culture vials has the potential to accelerate species identification of bacteria and improve clinical management. The aim of this study was to evaluate the ability of VitekMS to identify bacteria directly from positive blood culture vials. Methods. An aliquot of forty positive blood cultures were individually inoculated on gel separator tubes, centrifuged and washed with sterile water to obtain bacterial inoculum. For bacterial identification, protein extraction from the pellet was done by acetonitrile/formic acid procedure and mass spectrometry fingerprinting was performed by Myla®. In parallel, Phoenix® (BD Diagnostics) automated system was carried out for bacterial identification and susceptibility testing. Results. Bacterial identification was achieved by MALDI-TOF MS in 95% of the samples. These results were in agreement with Phoenix® identification in 65% and 75% at the species and genus level, respectively. Among Gram positive bacteria, 95% were identified by MALDI-TOF directly from blood culture vials, but only 63% and 73% were in agreement with Phoenix results at species and genus levels, respectively. Gram negative isolates were identified by MALDI-TOF in 100%, directly from blood culture vials, and 71% were in agreement with Phoenix results, at specie and genus levels. Three microorganisms were identified only by VITEK MS®, and one only by Phoenix®. The most discordant isolates were Staphylococcus spp. followed by Streptococcus spp. Conclusions. Although, VitekMS has presented low agreement rates when compared to Phoenix system, the correct identification could not be stablished, sine literature data showed MALDI-TOF as a more accurated system. Futher evaluation of the definitive bacterial identification should be carry out, however, VitekMS showed to be a rapid tool for early identification of bacteria directly from blood culture vials.